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authorHugh Dickins <hughd@google.com>2012-10-08 16:33:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-09 16:22:56 +0900
commite6c509f85455041d3d7c4b863bf80bc294288cc1 (patch)
tree50ccf8e339b219851ca7ad000379b1559415e354 /mm/truncate.c
parent39b5f29ac1f988c1615fbc9c69f6651ab0d0c3c7 (diff)
mm: use clear_page_mlock() in page_remove_rmap()
We had thought that pages could no longer get freed while still marked as mlocked; but Johannes Weiner posted this program to demonstrate that truncating an mlocked private file mapping containing COWed pages is still mishandled: #include <sys/types.h> #include <sys/mman.h> #include <sys/stat.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <stdio.h> int main(void) { char *map; int fd; system("grep mlockfreed /proc/vmstat"); fd = open("chigurh", O_CREAT|O_EXCL|O_RDWR); unlink("chigurh"); ftruncate(fd, 4096); map = mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE, fd, 0); map[0] = 11; mlock(map, sizeof(fd)); ftruncate(fd, 0); close(fd); munlock(map, sizeof(fd)); munmap(map, 4096); system("grep mlockfreed /proc/vmstat"); return 0; } The anon COWed pages are not caught by truncation's clear_page_mlock() of the pagecache pages; but unmap_mapping_range() unmaps them, so we ought to look out for them there in page_remove_rmap(). Indeed, why should truncation or invalidation be doing the clear_page_mlock() when removing from pagecache? mlock is a property of mapping in userspace, not a property of pagecache: an mlocked unmapped page is nonsensical. Reported-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Rik van Riel <riel@redhat.com> Cc: Michel Lespinasse <walken@google.com> Cc: Ying Han <yinghan@google.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/truncate.c')
-rw-r--r--mm/truncate.c4
1 files changed, 0 insertions, 4 deletions
diff --git a/mm/truncate.c b/mm/truncate.c
index f38055cb8af6..d51ce92d6e83 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -107,7 +107,6 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
cancel_dirty_page(page, PAGE_CACHE_SIZE);
- clear_page_mlock(page);
ClearPageMappedToDisk(page);
delete_from_page_cache(page);
return 0;
@@ -132,7 +131,6 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
if (page_has_private(page) && !try_to_release_page(page, 0))
return 0;
- clear_page_mlock(page);
ret = remove_mapping(mapping, page);
return ret;
@@ -394,8 +392,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;
- clear_page_mlock(page);
-
spin_lock_irq(&mapping->tree_lock);
if (PageDirty(page))
goto failed;

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